Apparatus for separating, washing and classifying solids



Feb. 6, 1962 H. LQEVENSTEIN ETAL 3,

APPARATUS FOR SEPARATING, WASHING AND CLASSIFYING SOLIDS 4 Sheets-Sheet 1 Original Filed Sept. 11, 1956 Fig. 5

Fig. 7

ATTORNEY Feb. 6, 1962 H. LOEVENSTEIN ETAL 3,019,895

APPARATUS FOR SEPARATING, WASHING AND CLASSIFYING SOLIDS Original Filed Sept. 11, 1956 4 Sheets-Sheet 2 Fig. 3

INVENTORS ATTORNEY Feb. 6, 1962 H. LOEVENSTEIN ETAL 3,019,895

APPARATUS FOR SEPARATING, WASHING AND CLASSIFYING SOLIDS Original Filed Sept. 11, 1956 4 Sheets-Sheet 3 i 1 HI llll (1) lfi' 5 92 T no |oo Fig.4

INVENTORS BY 'z /wfhv ATTORNEY H. LOEVENSTEIN ETAL 3,019,895

APPARATUS FOR SEPARATING, WASHING AND CLASSIFYING SOLIDS Feb. 6, 1962 .4 Sheets-Sheet 4 Original Filed Sept. 11, 1956 ATTORNEY 3,019,895 APPARATUS FOR SEPARATING, WASHING AND CLASSIFYIING SOLIDS Hirsch Loevenstein, Los Angeles, Calif., and Carl W. Carlson, Salem, and Leland B. Gunderson, Hood River, reg., assignors to Harvey Aluminum (Incorporated), a corporation of California Original application Sept. 11, 1956, Ser. No. 609,254, now Patent No. 2,964,179, dated Dec. 13, 1960. Divided and this application May 6, 1960, Ser. No.'27,303

3 Claims. (Cl. 20912) 3,519,895 Patented Feb. 6, 1952 of a slurry, thereby making possible transmitting the fines 1 to another processing sequence, e.g. back to a precipitator.

This invention relates to apparatus for separating, washing and classifying solids contained in a liquid slurry.

This application is a division of application Serial No. 609,254, filed September 11, now Patent No. 2,964,179,

for Separating, Washing and Classifying Solids and Conother aluminum minerals are digested with caustic soda in an autoclave. The resulting solution-of sodium aluminate is separated from the red mud residue, which then is washed with water. The clear, pregnant solution is diluted with water to hydrolyze the sodium aluminate and precipitate the aluminum as aluminum trihydrate. The latter then is separated from the solution, classified and further processed or applied to its various industrial uses. In this sequence of operations use advantageously may be made of apparatus such as is described herein'for separating the solids from the liquids, washing the solids, and classifying them.

Presently available methods and apparatus for performing the foregoing operations are relatively complicated, require apparatus of excessively high capacity and are not sufliciently flexible to permit carrying out easily a selected one or any combination of the operations in the same apparatus. Also, they do not permit the simultaneous separation, washing and classification of the solids. Still further, they require careful control and a relatively large number of skilled operators.

Accordingly, it is the general object of this invention to provide apparatus for separating, washing, and classifying solids which overcome the foregoing deficiencies of the prior art and which makes possible:

(1) The continuous separation of solids from a liquid. (2) The simultaneous separation and washing of the solids.

(3) The simultaneous separation, washing, and classification of solids.

(4) The separation of solids from a slurry without filtering the slurry.

(5) The separation of solids from a slurry without filtering the slurry and without withdrawing a significant amount of the liquid content thereof.

(6) Washing solids suspended in a liquid-while the solids are being separated therefrom, using a minimum quantity of washing liquid so as not to dilute the mother liquor unnecessarily.

(7) The separation of the fine from the coarse particles (8) The use of apparatus of simple, inexpensive design and comparatively small volume which occupies a minimum of space and does not include costly and bulky filters.

The manner in which the foregoing and other objects of this invention are accomplished will be apparent from the accompanying specification and claims considered together with the drawings, wherein:

FIG. 1 is a schematic sectional view in elevation illustrating the presently described apparatus for separating solids from liquids;

I FIG. 2 is a schematic sectional view in elevation illustrating another novel apparatus for separating solids from liquids;

FIG. 3 is a sectional view in elevation illustrating apparatus which combine features of the solids separating apparatus of FIGS. 1 and 2 and which may be applied also to the washing of the solids prior to their separation from the liquid;

FIG. '4 is a view in side elevation, partly in section, illustrating still another form of the invention wherein means. are provided for separating the solids and also for washing them;

FIG. 5 is a sectional view taken along line 55 of FIG. 4 and illustrating agitating means employed in the solids washing unit of the apparatus of that figure;

FIGS. 6 and 7 are detail views illustrating still further the agitating elements employed in the washing unit of the apparatus of FIG. 4; and

FIG. 8 is a sectional view in side elevation of still another form of the herein described apparatus wherein means are provided not only for separating and washing the solids but also for classifying them.

Generally stated, the present invention provides apparatus which functions by maintaining a liquid slurry in a vessel having an open end, forcing the slurry against the open end of the vessel and directing a stream of liquid across the open end in such a manner that the stream impinges upon the slurry in the vessel. The stream flow upstream from the open end is maintained at least equal to the stream flow downstream therefrom.

As a result, there is established a liquid seal across the open end of the vessel. This prevents substantial discharge of the liquid content of the slurry through the open end. However it permits entrainment of the slurry solids in the stream, thereby separating the solids from the liquid. I

If desired, the stream flow upstream from the open end of the vessel may be increased until it is greater than the ream flow downstream therefrom. As a result, surplus liquid will enter the vessel, washing the solids, and forming a second liquid stream.

Fresh slurry then may be introduced into the second stream at an intermediate point so that the fines will be washed away in the direction of stream flow while the heavies-may be forced in a countercurrent direction by gravity, or mechanically, into the vessel in which their separation from the liquid is elfectuated. In this manher the solids may be separated, washed and classified simultaneously in unitary apparatus.

Considering the foregoing in greater detail and with particular reference to the drawings:

3 THE SOLIDS SEPARATING APPARATUS OF FIGURE 1 Simple apparatus illustrating the herein described apparatus for separating solids from liquids is illustrated schematically in FIG; 1. A quantity of liquid slurry which may comprise an aqueous suspension of aluminum trihydrate is contained in a vessel 12. which has a tapered, preferably conical, bottom.

The bottom of the vessel is formed with an opening 14 preferably of restricted cross section. A conduit indicated generally at 16 extends across the opening at the bottom of the vessel, This conduit, although continuous, may be considered to comprise two sections. The first sectionlS is upstream from the opening; the second section 2% is downstream therefrom. I

A pump of suitable design, not illustrated, is connected to conduit 16 for pumping therethrough a stream of liquid which may be identical or different from the liquid contained in slurry 10. The pumped liquid may comprise, for example, liquid in which the solids are to be washed, or with which they are to be further reacted.

The stream of liquid through conduit 16 is controlled so that the flow through the upstream segment 18 is at least equal to the flow through the downstream segment 20 In this manner there is provided a liquid seal across opening 14 which prevents slurry 10 from flowing out through the conduit.

Consequently the solid particles present in the slurry gravitate downwardly in vessel 12 to opening 14. There they are entrained in the liquid streampassing through conduit 16 and separated from the liquor in the vessel without filtering and without removing a significant portion of the liquor.

THE SOLIDS SEPARATING APPARATUS OF FIGURE 2 To assist in the separation of the solids from the liquor, apparatus illustrated schematically in FIG. 2 may be employed. In this embodiment slurry 22 is contained in a vessel 24 which again has a tapered or conical lower portion and a restricted opening 26 at its bottom. This opening may communicate with a tubular chamber 28. A motor driven screw 39 is mounted for rotation in this chamber, longitudinally thereof.

Also, a motor driven, tapered packing or companion screw 32 is rotatably mounted in a vertical position in vessel 24. The flights of this screw may be of progressively reduced pitch and may be provided with a plurality of perforations 34. They touch or are spaced a short distance from the side walls of the vessel.

As screw 32 rotates in the indicated direction, it engages the solid particles contained in the slurry and forces them downwardly, thereby packing them together and squeezing out the liquor therefrom. The packing action of the screw is attributable to two factors: First, the progressively reduced pitch of the screw flights; and secend, the tapered configuration of the screw which works in a conical vessel. In many instances, the conical compression per so may be suflicient to induce the desired degree of packing. In such a case the screw flights need not be of progressively reduced pitch.

As the solids are packed in the bottom of the vessel, they form an ineffective seal which prevents substantial migration of the liquid content of the vessel out through opening 26, provided the amount of solids admitted to the apparatus per unit time remains substantially constant. It will be' apparent that if the solids input is reduced materially, the plug at the bottom of the vessel maybe broken, permitting passage of the liquid.

Upon continued operation of the apparatus, the solids which have been forced selectively toward the bottom of the vessel are driven into chamber 28, where they may be removed by motor driven screw 36. In this manner separation of the solids is achieved with very little of the mother liquor being carried away with them.

After being expressed from the solids by the action of the screw, the mother liquor flows upwardly toward the top of the vessel. During its progress, it either passes through perforations 34 in the flights of screw 32, through the space between the flights and the side Walls of the vessel if such has been provided, or through both the perforations and the space between screw flights and vessel side walls if both of these passageways have been provided. It should be noted that the herein described apparatus is flexible in this respect and that where suflicient clearance is afiorded between the screw flights and the side walls of the vessel, perforations 34 may be omitted altogether.

The solids separating apparatus of FIG. 2 thus affords a means of separating solids from a liquid wherein a plug of the separated solids serves the same purpose as the liquid seal of the embodiment of FIG. 1 in that it prevents migration of the liquid content of the slurry contained in the vessel from migrating out through the opening at the bottom thereof. However, in contrast to the apparatus of FIG. 1, the apparatus of FIG. 2 does not permit washing of the solids prior to their separation. Accordingly, although apparatus including the liquid seal may be used satisfactorily in some applications, in other applications it may be preferred to employ apparatus I which utilizes both the liquid seal and the packing screw.

Such apparatus is illustrated in FIG. 3..

THE SOLIDS SEPARATING AND WASHING APPARATUS OF FIG. 3

In the form of the invention illustrated in FIG. 3, the principles of the liquid seal and the packing or compression screw described above in connection with FIGS. 1 and 2 are used simultaneously not only for separating the solids from a liquid slurry, but also for washing the solids preliminary to their separation. To this end a slurry 40 is introduced into a vessel indicated generally at 42, the upper portion 44 of which is cylindrical in cross section and the lower portion 46 of which is conical and tapered downwardly. The conical bottom of the vessel is truncated to provide 'an opening 48 which corresponds to openings 14, 26 of the previously described forms of the: invention.

Slurry is introduced continuously into the vessell through conduit 50 which empties into a feedwell 521. An overflow launder 54 of convention construction is pro-- vided at the top of theivessel. It communicates with av conduit 56.

well 52. The working portion of the screw is housed in conical portion 46 of the vessel. It is provided with flights of gradually reduced pitch and with perforations 62.

if desired, the flights of the screw may be spaced slightly from the side walls of the vessel in which case perforations 62 may be omitted altogether. screw is tapered downwardly to conform to the tapered interior of the vessel. As has been described above with reference to the embodiment of FIG. 2, the action of the screw packs the solid particles present in the slurry in the region adjacent opening 48 in the bottom of the vessel.

As in the embodiment of FIG. 1, a liquid seal is provided at the bottom of vessel 42. The seal is formed by a conduit having, with reference to opening 48, an upstream section 64 and a downstream section 66. A pump 68' is provided in the upstream section of the conduit and another pump 70 in the downstream segment thereof. If desired, one of these pumps may be replaced with a valve.

In the continuous operation of the apparatus of FIG. 3, s urry 40 is introduced continuously through conduit 59 into feedwell 52 and thence into vessel 42. The separa- Also, the

tion of its components commences immediately, the solid particles gravitating downwardly until they reach the flights of screw 60.

When this occurs they are urged downwardly by the conical compression induced by the tapered configuration of the bottom portion of the apparatus and by the packing action of the gradually decreasing pitches of the screw flights. Liquor expressed from the solids escapes through perforations 62 or past the edges of the screw flights. Accordingly, the screw squeezes out almost all of the mother liquor from the solids and forms a thick paste which is discharged through opening 48.

During this sequence, the slurry in vessel 42 is prevented from running out opening 48 by a liquid seal. This is created by the stream forced by pumps 68, 70 through upstream conduit 64 and downstream conduit 66 and flowing past the opening. If the two pumps operate at the same speed the volume of the stream flowing through the upstream conduit will be substantially equal to that flowing through the downstream conduit. As a result, the paste forced through opening 48 by screw 60 is entrained in the stream and carried away, accompanied by only a negligible amount of mother liquor.

In this manner the solids may be separated effectively from the liquor. Such a separation might be useful, for example, in a two-step digestion process in which a solid after being digested in the first step must be separated from the pregnant liquid before being digested in the second step. In such a case the liquid introduced as the liquid seal may comprise the reagent to be used for the second digestion step.

As has been indicated above, not only may the solids be separated from the liquid content of the slurry, but they also may be washed prior to such separation. Thus they may bewashed continuously by adjusting the relative outputs of pumps 68 and 70 so that a greater amount of liquid is pumped by the former than by the latter.

The surplus liquid then will pass up through opening 48 in the conical portion 46 of vessel 42, through the perforations 62 in the fiightsof screw 60 and/or around the edges thereof, and up into the cylindrical portion 44 of the vessel. Duringits upward travel it washes the solids so that they become relatively free of mother liquor. It also mixes with the liquid component of the slurry and the resulting diluted liquor passes into overflow launder 54 and out through conduit 56.. Accordingly as products of this procedure there are formed a washed solid and a liquor which is free from solids and slightly diluted by the Washing liquid.

The operation of the apparatus of FIG. 3 is further illustrated by the following examples which illustrate the applicability of the apparatus in a two-stage digestion process in which a solid, after being digested in a first stage, must be separated from a pregnant liquid preliminary to being digested in a second stage.

Example 1 A calcium aluminate slag was digested in two stages with a sodium carbonate solution. After the first digestion stage the partially digested slag was separated from the pregnant liquor by continuously introducing the digestion mixture into vessel 42 of FIG. 3 through conduit 50.

A liquid seal was established at the bottom of the vessel by pumping fresh sodium carbonate solution through conduits 64, 66, the fresh sodium carbonate solution being the reagent to be employed in the second stage digestion of the mud. The amount of liquid passing through liquid seal conduit 64 was maintained substantially equal to that passing through liquid seal conduit 66. Also, the volume of solution continuously withdrawn through conduit 56 was maintained substan-' tially equal to the volume continuously introduced into the apparatus through conduit 50.

Accordingly, the solids content of the slurry introduced through conduit 50 settled downwardly in the vessel, being packed at the bottom thereof by the action of screw 60. There it was entrained by the sodium carbonate stream comprising the liquid seal and carried away for further digestion in a second stage.

The pregnant alumina-containing liquor leaving the apparatus via overflow conduit 56 was continuously clear and free from mud. That it was not diluted by the sodium carbonate solution used for the liquid seal was determined by repeated analyses of the solution entering the vessel via line 50, and that leaving the vessel via conduit 56. The results of these analyses are given in Table I below.

TABLE I Time Entering Leaving Example 2 This example illustrates the separation and washing of solid particles from a liquid slurry in which they are contained using the apparatus of FIG. 3.

A sodium aluminate solution resulting from the digestion of a slag with sodium carbonate was treated with carbon dioxide in a precipitator for precipitation of aluminum trihydrate. This formed an aluminum trihydrate slurry which was introduced continuously through line 5%) into the apparatus of FIG. 3. A liquid seal was established at the bottom of the apparatus by passing water through lines 64, 66. The mother liquor was withdrawn continuously through overflow conduit 56.

The feed rate of slurry through the apparatus through line 50 was 45 gallons per hour. Water waspassed through upstream liquid seal conduit 64 at a rate of 16.5 gallons per hour, and through downstream liquid seal conduit 66 at the rate of 15 gallons per hour Hence 1.5 gallons per hour of water were diverted upwardly through the apparatus, joining the mother liquor and passing with it out through overflow conduit 56. This resulted in effective washing of the alumina particles which were packed in the bottom of the apparatus by the operation of screw 60, while diluting the mother liquor only 3.3%.

During the operation of the apparatus the efiiuent water of the liquid seal and the solid aluminum trihydrate contained therein were analyzed periodically to determine their sodium oxide content. This gave a measure first of the loss of sodium oxide in the liquid seal Water and secondly of the purity of the alumina obtained as an end product. The results were as follows:

TABLE II N320 m Na 0 in Time Water A (g./l.) (percent) 3. (i8 .41 3. 45 38 3. 28 35 3. 75 31 10 p. 3. 72 41 11 p.111 3. 41 41 These figures establish conclusively that the aluminum trihydrate product has been effectively freed of sodium oxide without loss of a significant quantity of that reagent to the liquid seal water.

THE SOLIDS SEPARATING AND WASHING APPARATUS OF FIGURES 4, 5, 6 AND 7 rected across the opening and communicating therewith.

Apurnp 88 and another pump 96 which may be operated at the same or differential rates cooperate in establishing a stream of liquid across the opening, the volume of flow in the upstream conduit 84 being at least as great as that in the downstream segment 86.

A compression screw 92, which preferably is driven by a variable speed motor, works in vessel80. As before, the flights of this screw have a downwardly decreasing pitch and perforations 94 are provided to permit the passage of liquid through the flights.

A conduit 96, which communicates with the lower :portion of the vessel, permits the introduction of-additional :quantities of liquid into the vessel for a purpose which will appear hereinafter.

The upper portion of vessel 80 communicates with a washing chamber which preferably comprises a tube 100. This tube is inclined downwardlyin the direction of vessel 80. For best operation, the degree of inclination is not less than 2 nor more than 45. It is provided with means for agitating a slurry as it passes through the tube. In the illustrated form, the agitating means comprise a shaft 102 which is suitably mounted in bearings 104,

106 and which is rotated in the indicated direction by a variable speed motor. Mounted on the shaft are a plurality of shovel-shaped agitators 110, the construction of which'is detailed in FIGS. 5, 6 and 7. Each of the agitators is made up of three plates. One of these, plate 112, is fixed to shaft 102. Another, plate 114, is roughly triangular in outline and is welded to the-end of plate 112 at a substantial angle thereto. The apex of this plate is adjacent shaft M2.

The third plate 116 is welded to plates 112, 114 in such amanner thata shovel-like recess is provided. The inclination of the agitators on the shaft is such that sedimentar.y solids on the bottom of the tube are picked up by the agitators, moved upwardly, and released, whereupon they ;percolate down through the liquid contained in the tubeand are washed eiiectively.

A conical or cylindrical settling vessel 120 comm-unicates with the upper end of tube 1%. This vesselis provided with a feedwell 1221mm which slurry may be passed by means of infeed conduit 124. It also is equipped with an overflow launder lldwith outlet 123, this being of conventional construction.

The operation of the continuous combination separation and washing apparatus of FIGS. 47 is as follows:

A liquid seal is established at the bottom of separating vessel 80 by establishing a flow through conduits d4, 86 such that the flow through conduit 84 is at least as great as that occurring through conduit 86. Where the solids are to be washed as well as separated, the flow through upstream conduit 84 is increased until it is greater than that passing through downstream conduit 86.

Only a small amount of excess liquid need be introduced in this manner. In the usual case the amount thus introduced does not exceed 10% of the volume of the slurry.

If it is desired to augment the amount of washing water thus admitted additional water may be introduced in predetermined amounts through conduit 96.

The excess liquid mixed with the liquid separated from the slurry passes upwardly through separation vessel 30, through washing tube 100, through settling vessel 120 and out through overflow launder 126.

As a slurry or other liquid mixture containing suspended solid particles is introduced into settling chamber 120 via conduit T124 and feedwell 122, the solid particles which it contains gravitate downwardly through the settling chamber while the clear liquor remaining passes upwardly through the overflow launder 126 together with the excess wash liquor introduced through conduits 84 and 96. V

The particles next enter downwardly inclined washing tube 10% where they continue their gravitationally impelled downward course.

They are assisted in their travel, and washed by the action of the shovel-shaped agitator blades 110 on shafit 192. These scrape the particles from the bottom of the tube, lift them upwardly and backwardly and release them near the top of the tube so that they percolate downwardly through the liquor in the manner described above.

The washed particles then pass into the top of conical separation vessel 80. There they continue to move downwardly, being assisted by the action of compression screw 92. As they descend, they meet the fresh wash liquor introduced through conduits 84 and 96 and accordingly are Washed further. When they reach the "bottom of the vessel, they are entrained in the sealing stream of liquid passing through conduits 84, 86 and thus removed without removing an important amount of the liquor, liquor losses being kept under 1% in a typical instance.

The operation of the apparatus of FIGS. 4-7 is further illustrated by the following examples: I

Examples 3 N This example illustrates the operational efliciency of the apparatus of P168. 4-7 with and without the liquid seal applied.

A calcium aluminate slag was digested with sodium carbonate to form a slurry composed of a mud suspended first a liquid seal was not established at the bottom of separating chamber 8t). Instead, wash water was introduced in conventional manner through a conduit (not illustrated) communicating with the lower end of washing tube 1%. Wash water in suitable amount was introduced continuously into the apparatus through this tube and withdrawn continuonslyfrom the bottom of separator 80.

After an operating period of 4 hours the flow of water through the conduit communicating with washing tube 1% was cut oil and a liquid seal established at the bottom of separator 50 by establishing a flow of water through liquid seal conduits 84, $6. The flow through conduit 84 was maintained slightly greater than that through conduit 86. Accordingly part of the water was diverted upwardly through separator and washing tube 16!), where it washed the solids content of the slurry, and thence into settling chamber 129 where it joined the liquor discharged through overflow'conduit 128. The solids, in turn, after being washed in tube 1%, passed into separator80 where they were packed by the action of screw 2 and carried away by the water stream in conduits 8d, 36.

To .test the efiiciency of the apparatus with and without the liquid seal applied periodic determinations were made of the sodium oxide content of the feed slurry entering the apparatus through conduit 124, of the liquor leaving the apparatus through conduit 128, and the water 9 leaving the apparatus through conduit 86 of the liquid seal. The results are set forth in Table III below.

TABLE III a WITHOUT LI UID SEAL From a consideration of the foregoing values, it is apparent that when the herein described liquid seal is not applied and the wash water passes through the apparatus in the conventional manner, a very substantial amount of sodium oxide is lost to the wash water. Also, the liquor separated from the solids is diluted to a high degree. However, when the liquid seal is applied, loss of sodium oxide to the efiluent water is negligible and only slight dilution of the liquor occurs.

Example 4 This example, considered together with Examples 5 and 6 below, demonstrates that the liquid seal flow rate may vary substantially without significantly affecting the efficiency of the solids washing and separating operations.

The procedure outlined in Example 3 above was repeated using the liquid seal. A slurry composed of a mud suspended in a sodium aluminate liquor containing excess sodium oxide was fed continuously to the apparatus through conduit 124 at a rate of 60 gallons per hour. Water was passed through the liquid seal at a rate of 180 gallons per hour. At periodic intervals the sodium oxide content of the slurry fed-into the apparatus through line 124, of the liquor leaving the apparatus through line 128, of the water leaving the apparatus through line 86, and of the mud discharged from the bottom of separating cylinder 80 was determined. The results are given in Table IV.

It thus was found that the loss of sodium oxide in the eflluent water was 3.08% and in the mud 2.3% by weight. The dilution by the wash water of the liquor leaving the apparatus varied between 1.38% and 14.4%, the average being 7.15%.

Example 5 This example illustrates the application of the. apparatus of FIGS. 4-7 using a somewhat reduced water flow through the liquid seal.

The procedure of Example 4 was repeated using, however, a flow of 120 gallons per hour of water through liquid seal conduit 86 instead of the flow of 180 gallons per hour employed in the procedure of Example 4. The results were as follows:

TABLE V N 3.20 content in grams per liter Time Mud,

Liquid Seal percent Slurry Liquor Efliuent Water In this case the loss of sodium oxide in the liquid seal effluent water was 3.86% and in the mud 1.6% by weight. The dilution of the liquor leaving the apparatus varied between 1.87% and 21.8%, the average being 13.8%.

Example 6 The procedure of Example 4 again was repeated using, however, a stream flow in the liquid seal conduit of about 60 gallons per hour. The results are given in Table VI below.

TABLE VI N 8.10 content in grams per liter Time Mud,

Liquid Seal percent Slurry Liquor Effluent Water i It will be seen from a consideration of the foregoing values that when the liquid seal flow was but 60 gallons per hour, the loss of sodium oxide inthe liquid seal eflluent averaged 1.38% and in the mud 2.1% by weight. w The extent of dilution of the liquor leaving the apparatus varied between 2.62% and 19.1%, the average being Also, from a comparison of the results set forth in Examples 4, 5 and 6 it will be apparent that the efficiency of the liquid seal utilized in the herein described apparatus is maintained even though the amount of liquid used in maintaining the seal is varied over wide limits.

THE SOLIDS SEPARATING, WASHING AND CLAS- SIFYING APPARATUS OF- FIGURE 8 Still another form of our invention is illustrated in FIG. 8. In this embodiment means are provided not only for separating and washing the solids, but also for classifying them. I

The FIG. 8 apparatus is similar in many respects to that of FIG. 4. 'Thus it includes a separation vessel which maybe substantially identical with vessel 80 of FIG. 4. It is generally conical in shape and provided with a restricted opening 142 at its lower end.

A compression screw 144 works in the vessel. This screw has perforations 146 through its flights and/or enough clearance to afford a passageway for the liquid moving upwardly through the vessel. In addition, the flights are tapered to conform to the contour of the cone, which they almost touch, and are of reduced pitch as they descend therein. A conduit 143 communicates with the vessel just above the opening in therbottom thereof.

Also, a liquid seal such as is described in the previously described embodiments is present. This is formed by means of communicating conduits 150, 152 which are upstream and downstream, respectively, from opening 142. Jumps 154, 156 are present in the line and are controlled in such a manner as to insure that the flow through the upstream conduit 150 is at least equal to that of the downstream condu-it 152. Accordingly a liquid seal is estab- -lished and the liquor in vessel 140 is prevented from entering the conduit.

A combination washing and classification chamber is associated with separation vessel140. This chamber comprises an inclined tube 160 sealed at both ends and communicating with vessel 140 at its lower end. The angle of inclination of tube 164} is a function of the difference in size between the fine and coarse particles of the slurry and hence may be predetermined as required for processing a given slurry.

Agitating means for agitating solids contained in the tube are-provided and comprise a shaft 162 rotatably mounted in bearings-164, 166 and coupled to a variable speed motor which drives it in the indicated direction.

Two classes of elements are mounted on the shaft. The first, indicated generally at 168, comprises shovelshaped agitating elements which are stationed in the lower portion of the tube and may be identical with elements 110 mounted on shaft 102 of FIG. 4.

Thus these elements comprise three plates welded together and including plate 170 which is rigidly fixed to the shaft, plate 172 which is fixed to the outer edge of plate 170 at a substantial angle thereto and triangular plate 174 which interconnects the foregoing two plates. These agitators are arranged on the shaft at an angle calculated to scrape solid material from the bottom of the tube, lift it, move .it backwardly (to the right as viewed in FIG. 8) and release it near the top of the tube so that it settles down through the liquid contained there- The second class of elements present in the upper portion of tube 160 comprise driving plates 180 which may be similar to or identical with plates 170 of shovel agitators 16 8. Their purpose is to move the coarser grains contained in the slurry slowly downwardly in the tube without lifting them upon the liquid. Hence the inclination of driving elements 180 is just the opposite of that of agitators 168 so that the coarse particles which they engage are forced against the current in the tube until they come withinthe sphere of activity of agitators 168.

The relative proportion of tube 160 which is occupied by shovel agitators 168 and driving plates 180 is somewhat variable, depending upon the proportion of fine and heavy particles contained in the slurry to be treated. Whatever the proportion, a conduit in the form of a standpipe 182 fed with fresh slurry from pipe 184 communicates with the tube at substantially the point of junction of the two types of elements.

The upper terminus of tube 160 communicates through connector 186 with a thickener or settling vessel 188. This is of conventional construction and is provided with anoverfiow launder 1% for removal of liquid. Its bottom is conical and communicates with a pump 192 by means of which thickened solids composed of the fines are removed.

The operation of the combination apparatus of FIG. 8 is as follows:

The apparatus is filled with slurry which is to be treated and a liquid seal established at opening 142 by pumping a stream of liquid, for example, a liquid to be used for washing and conveying the separated slurry solids, through conduits 150, 152. Pumps 154, 156 are regulated so that the volume of liquid passing through conduit 15% is greater by a predetermined amount than that passing through conduit 152. Hence the liquid contents of separating chamber 140 are prevented from passing out through opening 142.

Also, the excessliquid passes from conduit 15% through opening 142 into vessel 140;, where it mingles with additional liquid introduced through conduit 148, if any is thus admitted and washes the solids. The liquid passes 'in a continuous stream upwardly through the washing segment of tube 160, through the classifying segment of i2 tube 161} through thickener 188 and out through overflow 190.

Fresh feed comprising a liquid containing suspended solid particles is introduced into standpipe 182 from conduit 184. The solid particles of'the feed gravitate downwardly into tube 161% There the fines are entrained in the aforementioned stream through the tube and are carried into thickener 188 where they are separated in the usual manner. Thereafter they may be removed by pump 192 and returned to the operation for further crystal growth, or separated from the liquid in a separator such as is shown in FIG. 3.

The heavier solids gravitate down toward the bottom of tube 160 where they are engaged first by paddle elements 18%. These force them down to the lower section of the tube where they are picked up by shovel agitators 168. As has been discussed above, these scrape the particles from the bottom of the tube, lift them, carry them backwardly a short distance and release them so that they fall down through the liquid. This washes them and gives the liquid stream through the tube an opportunity to entrain the lighter particles and carry them into the thickener 188.

The heavy particles, on the other hand, ultimately reach the lower end of tube and pass into the top of separating vessel 140. There they gravitate downwardly, be-

ing assisted by the packing action of compression screw 144 which forces them down toward opening 1 2 at the lower end of the vessel. There they are entrm'ned in the liquid seal stream flowing in communicating conduits 150, 152 and carried away.

In this manner the slurry introduced into the appa ratus through standpipe 182 is processed for separation of the solid particlesand for contemporaneously wash ingthem to free them from the mother liquor and classifying them into fine and coarse particles, the degree of such classification being controlled as required by pre= determining the point of introduction of the slurry into tube 160.

Hence it will be apparent that by the present invention we have provided apparatus for separating, washing and classifying solid particles contained in a liquid medium, for example, aluminum trihydrate particles contained in a slurry. The apparatus is adapted to large scale, continuous operation. The separating, washing and classify= ing operations are carried out contemporaneously. Furthermore, the apparatus is simple in construction, does not include bulky filter units, and occupies a minimum of space. Also, in spite of the fact that filtration steps are not involved, a clean separation of the solids from the liquid is achieved without loss of a significant amount of mother liquor.

It is to be understood that the form of our invention herewith shown and described is to be taken as a preferred example of the same and that various changes in the shape, size and arrangement of parts may be made without departing from the spirit of our invention or the scope of the subjoined claims.

Having thus described our invention, we claim:

1. Apparatus for washing solids which comprises a downwardly inclined cylinder, means for introducing a slurry into the top portion of the cylinder, washing liquid inlet means for introducing washing liquid into the bottom portion of the cylinder for passage toward the top end of the cyiinder, means for withdrawing the washing liquid from the top end of the cylinder, a motor driven shaft rotatably mounted lengthwise of the cylinder, and a plurality of shovel-shaped blades arranged on the shaft for engaging settled slurry solids, the blades being disposed obliquely with respect to the axis of the shaft with the trailing end of the blades extending toward the top end of the cylinder to lift the settled slurry solids upwardly and toward the top end of the cylinder and then releasing them as the shaft rotates, thereby permitting a 13 the washing liquid to wash the solid material, and control means in the washing liquid inlet means for regulating the upward flow of said liquid such as to wash the solids content of the slurry as the solids progress downwardly toward said inlet means.

2. Apparatus for washing and classifying the solids content of a liquid slurry which comprises a downwardly inclined cylinder, washing liquid inlet means including control means for introducing washing liquid into the bottom portion of the cylinder for passage toward the top end of the cylinder in a flow suificient to carry upwardly therewith the fine solids content of the slurry, means for withdrawing the washing liquid from the top end of the cylinder, a motor driven shaft rotatably mounted lengthwise of the cylinder, a plurality of shovellike agitating blades arranged on the lower portion of the shaft for engaging settled slurry solids, lifting them upwardly and toward the top end of the cylinder and then releasing them as the shaft rotates, thereby permitting the washing liquid to wash the solid material and to carry fine solids with the washing liquid flow, the heavier solids gravitating downwardly countercurrent to the washing liquid flow, a plurality of driving blades arranged on the upper portion of the shaft for forcing solid material deposited in the upper portion of the cylinder into the field of action of the agitating blades, and means for introducing a slurry into the cylinder at a point substantially adjacent the point of juncture of the agitating and driving blades.

3. Apparatus for washing solids which comprises a downwardly inclined cylinder, means for introducing a slurry into the top portion of the cylinder, Washing liquid 14 inlet means for introducing washing liquid into the bottom portion of the cylinder for passage toward the top end of the cylinder, means for withdrawing the washing liquid from the top end of the cylinder, a motor driven shaft rotatably mounted lengthwise of the cylinder, and a plurality of shovel-shaped blades arranged on the shaft for engaging settled slurry solids, each of the blades comprising a first plate secured to the shaft and projecting therefrom in a plane disposed obliquely with respect to the axis of the shaft with the trailing end of the plate extending toward the top end of the cylinder, a second plate of substantially triangular shape secured to the first plate along the trailing edge of the latter with the apex of the second plate disposed adjacent the shaft and the edge opposite the apex disposed adjacent the outer end of the first plate and extending toward the top end of the cylinder, and a third plate secured to the outer edge of the second plate and leading edge of the first plate, the plates thereby forming a shovel-like recess therebetween for lifting the slurry solids upwardly and toward the top end of the cylinder and then releasing them as the shaft rotates, thereby permitting the washing liquid to: wash the solid material, and control means in the washing liquid inlet means for regulating the upward flow of said liquid such as to wash the solids content of the slurry as the solids progress downwardly toward said inlet means.

Grier Jan. 18, 1916 Day Dec. 2, 1919 

